Cellular telephone systems are widely used in a variety of applications and locations, including for communication from automobiles. In order to provide the greatest possible portability, the handset, or Personal Station, of a cellular telephone system is typically self-contained, receiving power from its own internal battery. The power provided by the battery is limited, particularly due to the need for a small battery in order to reduce the size and weight of the Personal Station.
In order to increase the operational power of the Personal Station, many users install booster stations in their automobiles. A further advantage of such an installation is that it takes advantage of the electrical power produced by the automobile. This increased power can greatly extend the range of the Personal Station.
According to the standards governing cellular equipment, all Personal Stations are classified according to the level of RF power they transmit. The goal of the booster's design is to convert the Personal Station (usually a Class II unit) into a higher class (usually a Class I) combination. At the same time, according to the same standards, each class of Personal Stations is divided into a number of power levels. To meet the standards requirements, the booster has to provide a required value of output power for each power level.
In order to keep an RF signal at a predetermined level, the value of the output RF is typically converted to a DC voltage. This voltage is applied to a first input of an operational amplifier. The second input of the operational amplifier is kept at a constant reference level voltage. Under these conditions, the signal from the output of the operational amplifier is controlled as necessary. In order for this system to operate, the power level of the input signal supplied to the first input of the operational amplifier must be supplied or predetermined. The reference level at the second input of the operational amplifier is chosen to correspond to that power level.
If the level of the RF input signal changes, the operational amplifier reference level should change accordingly. Thus, each of the RF output power levels should have a specific corresponding DC value to be used as an operational amplifier reference level.
In RF boosters of the prior art, the operational amplifier reference level is set by the Personal Station. This has the advantage of simplicity of implementation, as the level information is readily available from the Personal Station. However, setting the reference level at the Personal Station makes the booster dependent on a specific telephone model. It is difficult to adapt the booster to other types of telephones. Moreover, setting the reference level at the Personal Station provides the values of the "desired" signal. There is no provision to make sure that the RF signal transmitted by the Personal Station actually reaches the input of the booster.
There exists, therefore, a need in the art for a booster in which the reference level is easily adaptable to different types of telephones, and which provides that the signal transmitted by the Personal Station reaches the input of the booster.